Substitution of conventional mold lubrication by using self-lubricating raw parts in sinter forging II

• Applicant: Professor Dr.-Ing. Bernd-Arno Behrens
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 264818458

In cold forging, the semi-finished steel products are usually subjected to a phosphating process to produce lubricant carrier layers in order to withstand the high stresses during forming. The alternative method of powder metallurgically manufactured and subsequently infiltrated semi-finished products investigated here offers the potential to dispense with this costly, time-consuming and, in particular, environmentally harmful process.In the first funding period, it was shown that PM semi-finished products infiltrated with lubricant are generally suited for substituting die lubrication in cold forging. The lubricant leaks out during the forming process and lubricates the active tool surfaces, thus achieving comparable degrees of deformation to conventional die lubrication and simultaneously compacting the workpieces. It was found that a special adjustment between powder material, lubricant (viscosity, wetting angle) and porosity was required. Particularly promising in this context are a larger potential lubricant reservoir (sufficiently high porosity) and thus higher infiltrated lubricant, as well as a lubricant with a very low viscosity and a small wetting angle towards the powder material. Consequently, in the second funding phase, the choice of lubricant and the compromise between the highest possible porosity and sufficient formability should be optimized. Among other things, further lubricants will be investigated and the infiltration time significantly increased. Furthermore, an extrusion process will be applied which meets the requirements for high sliding paths and surface enlargements and which is also suitable for determining friction factors. The latter will be determined using the GTN model, which includes the plastic behavior of porous materials. In addition, the question of the whereabouts and possible use of the lubricant after forming arises. This question will be systematically investigated with the aim of achieving both the complete escape and the obtainment of the highest possible residual lubricant in the formed workpiece. Application examples can be found for both extremes, which are to be validated here on a laboratory scale. For example, a conventionally cold extruded shaft is usually subjected to high dynamic stresses, for which on the one hand a fully compacted material without residues is necessary. On the other hand, impact extrusion of hydrodynamic bearings or bearing bushes would be possible, which have an additional lubricant reservoir in the running surfaces and thus improved emergency running characteristics. As a reference, the forming tests and characterizations will also be carried out with conventionally coated solid semi-finished products and the results of the alternative method will be compared.

• DFG Programme: Research Grants